It's not letting him go that's the issue, it's the dirty way they've done it and treated him. They've sat silent all year and let Ty take the blame for everything instead of doing a little PR or letting him explain his decisions during press conferences like Sloan used to.
Ty has done everything asked of him by management, and he's been an exceptional developmental coach to the young guys (even that crybaby Enes Kanter). His thanks was a destroyed legacy, mostly by folks who frankly don't have the first clue about anything basketball (I'm looking at you SLC Dunk). When you have a group of people with nearly zero basketball knowledge who are ruining the legacy of your coach you have a responsibility to do a little more for the guy. Instead, they're happy to let him shoulder all the blame.
Such is the life of a very well paid, public figure.